Infrared and terahertz in biomedicine
A number of potential advances of infrared and terahertz technologies in application mainly to biomedicine are shortly discussed. In spite of the fact that there are a number of well-established imaging and spectroscopic techniques in application to biomedicine, there exist some problems where IR an...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2017
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| Цитувати: | Infrared and terahertz in biomedicine / F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 273-283. — Бібліогр.: 79 назв. — англ. |
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| citation_txt | Infrared and terahertz in biomedicine / F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 273-283. — Бібліогр.: 79 назв. — англ. |
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| description | A number of potential advances of infrared and terahertz technologies in application mainly to biomedicine are shortly discussed. In spite of the fact that there are a number of well-established imaging and spectroscopic techniques in application to biomedicine, there exist some problems where IR and THz technologies are the challenging technologies that can provide information not available from other techniques. E.g., they can be applied in cases where there is a need to improve the surgical removal of cancer, strictly locating tumor margins when conservation of normal tissue is needed.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
doi: https://doi.org/10.15407/spqeo20.03.273
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
273
PACS 87.50.U-, 87.64.km, 87.80.Dj, 87.85.Ox
Infrared and terahertz in biomedicine
F.F. Sizov
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03680 Kyiv, Ukraine, e-mail:sizov@isp.kiev.ua
Abstract. A number of potential advances of infrared and terahertz technologies in
application mainly to biomedicine is shortly discussed. In spite of the fact that there are a
number well established imaging and spectroscopic techniques in application to
biomedicine there exists some problems where IR and THz technologies are the
challenging technologies that can provide information not available from other
techniques. E.g., they can be applied in the cases where there is a need of improving the
surgical removal of cancer, strictly locating tumor margins when conservation of normal
tissue is needed.
Keywords: infrared and terahertz technologies, biomedical application.
Manuscript received 03.07.17; revised version received 14.08.17; accepted for
publication 06.09.17; published online 09.10.17.
1. Introduction
Infrared (IR) and especially terahertz (THz) technologies
have become one of the major fields of applied
researches to a great degree driven by potential
applications in biomedicine.
The IR technologies in applications to biomedicine
are known since 1950s. Concerning the THz area, a
simple search with keywords involving “terahertz” and
the traditional terms “far infrared” and “sub-millimeter
waves” comes up with thousands of hits (see, e.g.,
Fig. 1). Here, the current manuscript will be to a great
degree limited, since the author considered, the most
important developments in IR and THz technologies in
application to biomedicine. Numerous groups have now
demonstrated biomedical applications in distinguishing
healthy tissue from tissue with a disease or injury
resulting in modifications in protein structure or
salt/protein content, in cells of breast cancer, colon
cancer, burn imaging, and some other applications [1].
It can be noted that in 1990s the interest in THz
biological and medical effects in the former Soviet
Union Countries exceeded (at least by the number of
publications) than that one in other countries [2].
Especially in the THz area, recently, there has been
flurry of research of terahertz applications, which
includes THz imaging and spectroscopy for biomedical,
military, security, food and drug control applications,
etc.
For a long time, the terahertz range was considered
as a final frontier of the electromagnetic spectrum. It was
mainly related with difficulties in generating terahertz
radiation. Now, radiation frequencies between 0.2 and
10 THz have become to a great extent the domain of
optoelectronic laser-based techniques. Still other types
of THz sources (IMPATT diodes, BWO sources, Gunn
oscillators, quantum cascade lasers, gas and free-electron
lasers, etc.) play an important role in THz technologies.
Basic progress in THz imaging and spectroscopy is
related just with optoelectronic approaches that use
either femtosecond lasers or diode lasers to get tunable
THz radiation. Photomixers, photoconductive switches
or nonlinear crystals convert the near-infrared laser
radiation into terahertz waves, either broadband or
spectrally resolved.
Scientific and particularly application activity in IR
and THz technologies have increased significantly in
recent two decades, and it is to be expected that the
trends especially in THz science and technology will be
only continued and extended.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
doi: https://doi.org/10.15407/spqeo20.03.273
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
274
Fig. 1. Chronological chart (1960-2013) and exponential fits
(1960-2012) for the numbers of publications with topics
involving “terahertz” and the traditional terms “far infrared”
and “sub-millimeter waves”. The box shows the logarithmic
plot between 1970 and 2012 [3].
In addition to the well-known technical oppor-
tunities, historical examination of Internet usage as well
as the number of publications and patent applications,
confirms ongoing interest in this technique (Fig. 1).
Activity of THz technologies is noticed by annual
growth rate in between 9% and 21% [3].
2. Transparency and spectral regions
A shift from the scientific to more application-oriented
researches can be observed both for IR, THz and
microwave spectral regions. As concerning the
microwave region, the advantages of microwave remote
sensing consist in all-weather, day-and-night imaging
capacity as compared to IR remote sensing for which,
e.g., cloudiness prevents the Earth surface observation,
though the spatial resolution for this spectral region is
much higher, and IR thermal remote sensing is the
passive one as compared to microwave remote sensing
that is active for Earth surface observation.
For THz region, atmospheric absorption is too large
for remote sensing (see Figs. 2 and 3). Active micro-
wave sensing (realized using radars) is based on the
transmission of longwave microwaves (λ ~ 3–25 cm, ν ~
10–1.2 GHz) through the atmosphere and then recording
the amount of energy backscattered from the terrain.
Attention to energy consumption problems is rai-
sing the interest for the applications of thermal remote
sensing in urban environments. E.g., advances in thermal
infrared detectors and techniques have facilitated ob-
taining high-resolution thermal images over large areas,
for a correct quantitative evaluation of land surface tem-
peratures [5]. In the THz spectral region, the atmosphere
absorption is high (Figs. 2 and 3), which prevents to
apply long-distance THz technologies (see Fig. 4).
There is no commonly agreed definition of the
upper and lower frequency limits of terahertz THz and
infrared IR radiation and one can meet several different
segmentations of IR and THz spectral regions. In many
cases (see, e.g., [8]) today, the IR region is taken as the
region with the wavelengths λ approximately between 0.7
and 20 µm. From λ ~ 0.7 to 1.1 µm, it is the NIR (near
H O2
H O2
H O2
H O CO2 2
H O2
H O
7.5 g/m
2 3
H O2
Fog (0.1 g/m )
Visibility 50 m
3
Drizzle
(0.25 mm/h)
CO2
CO2
O2
O2
O2
Excessive rain
(150 mm/h)
Heavy
rain
(25 mm/h)
10 GHz 100 1 THz 10 100 1000
3 cm 3 mm 0.3 mm 30 m 3 m 0.3 mμ μ μ
20 C
1 atm
o
Frequency
Wavelength
A
tte
nu
at
io
n
(d
B/
km
) -
O
ne
w
ay
10-2
10-1
100
101
102
103
Terahertz
Millimeter Submillimeter Infrared V isible
Fig. 2. Transparency of Earth atmosphere from visible to radiofrequency band region [4]. Also are shown spectral radiances for
ideal black body for temperatures T ≈ 6000 K (Sun) and T ≈ 300 K (Earth surface). It is seen that strong water and oxygen
absorption in the atmosphere make high altitude platforms essential for good seeing of space objects.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
doi: https://doi.org/10.15407/spqeo20.03.273
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
275
IR) region, from λ ~ 1.1 to 2.5 µm it is the SWIR (short
wavelength IR) region, from λ ~ 2.5 to 7.0 µm it is the
MWIR (medium wavelength IR) region, from λ ~ 7.0 to
15.0 µm it is the LWIR (long wavelength IR) region and
from λ > 15.0 µm is the VLWIR (very long wavelength
IR) region. In other classifications, the IR spectra are
taken for the wavelengths from λ ~ 0.7 to 1000 µm
[9, 10]. Here, it is accepted that IR spectra lie within the
wavelengths range λ ~ 0.7 to 30 µm. In most applicable
for thermovision IR spectral regions 3 to 5 µm and 7 to
14 µm, atmosphere is transparent (Fig. 5).
Fig. 3. Transmission of THz radiation in air [6]. In THz active
imaging systems emission radiation frequencies should be
inside an atmospheric transmission windows to avoid strong
water vapor absorption.
Fig. 4. Predicted range to identify a concealed weapon using a
single scanning spot sensor [7].
Fig. 5. Typical atmosphere transmission over 1 km path length [11].
As concerning the THz spectrum, there exist
several classifications especially in the low frequency
part of THz spectra – the millimeter-wave region. The
millimeter-wave region of the electromagnetic spectrum
is generally taken to range from 30 GHz (λ = 1 cm) to
300 GHz (λ = 1 mm) [12] and even wider [13], while the
terahertz region is now frequently considered to be
between the radiation frequencies ν = 0.1 THz
(λ = 3 mm) and ν = 10 THz (λ = 30 µm) (see, e.g., [14-
17]), leaving the region of overlap between 0.1 THz
(λ = 3 mm) and 0.3 THz (λ = 1 mm).
Now frequently terahertz region is considered to be
between 0.1 THz and 10 THz [1, 17, 18]. Partial
overlapping with THz range is frequently used as the
term “far-infrared” [19, 20] (FIR, VLWIR), which is
often taken from 100 to 1000 µm (see, e.g., [9, 10]). The
range placed between frequencies from 300 GHz to
3 THz is usually called as the submillimeter-wave band
[21], though in this paper the terms “terahertz” and
“submillimeter-wave” are considered to be synonyms.
Here, it is accepted that THz spectra lie within the
radiation frequencies between 0.1 and 10 THz (from
(λ = 3 mm to 30 µm).
As to THz radiation frequency range, it is known
that many materials that are opaque to visible and
infrared light are transparent to THz radiation [22-24]
(paper, foams, plastic, textiles, etc.). Attenuation values
(in dB) for some clothing, fabric, and building materials
in the radiation range 94–1042 GHz are presented in
[25]. THz imaging was applied for non-destructive
quality check of hidden damages in foams after accident
in 2003 with Space Shuttle Columbia.
THz radiation is heavily absorbed by water.
Another feature of THz radiation frequency is that the
fundamental frequencies – rotational and vibrational
modes of molecules like proteins or DNA – are located
in this region (see, e.g., [21, 26, 27]). This gives the
opportunity to control content of materials under
investigation by using the known fingerprints of
substances.
Because of the relatively large width of the THz
spectra, which exceeds, for example, the visible light
range (λ ~ 0.4–0.7 μm) and is close to the wide band of
IR radiation (~0.7–30 μm), THz radiation is of great
importance in terms of fundamental researches as well as
in technology and life sciences, as in this region
rotational and vibrational lines of a lot of substances are
located. All the applications require different THz
detector sensitivities and source capabilities, closely
related to temperature exploitation and different spectral
band applicability. These circumstances should be taken
into account in estimations of THz systems cost that may
differ several orders.
3. Applications
Typical IR technologies applications can be separated in
two major groups. On the one hand, there are NIR and
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
doi: https://doi.org/10.15407/spqeo20.03.273
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
276
SWIR spectral regions, which are commonly employed
for the assessment of artworks (e.g., paintings and
frescoes), since some painting pigments are semi-
transparent to the infrared in these spectral bands and
some other are not (e.g., carbon based). In this region,
also IR spectroscopy is applied in biomedical science.
On the other hand, there is infrared thermography, which
involves detection of the surface and subsurface layers
of objects on the differences in thermal signatures in the
MWIR and LWIR spectral bands. In biomedicine
applications mostly thermography and spectroscopy are
applied in any IR band [28].
THz waves are sufficiently short to provide
resolution of less than 1 mm (far field approximation)
and several hundred nanometers for solid-state objects
[29] (near field approximation), yet long enough to
penetrate most nonmetallic substances, such as materials
used to make clothing, rucksacks and tarps [25]. As
such, they are useful to security agents and military
personnel alike for revealing concealed weapons,
chemical explosives and biological agents. Besides,
security applications, namely: airport screeners, higher-
resolution terahertz sensors, could provide enhanced
identification of battlefield targets, better missile
guidance and other combat advantages [3]. Soldiers,
marines and fighter pilots are increasingly trained to use
not only the visible wavelengths that their eyes can
process, but infrared wavelengths as well, the
application fields of which are widespread in military
and civil domains. But contrary to IR region where
imaging as a rule is passive, due to the lack of
appreciable terahertz power in the thermal background,
it is necessary to use an illumination (THz sources) for
imaging.
The increasing demand of unoccupied and
unregulated bandwidth for wireless communication
systems will lead to extension of operation frequencies
toward the lower THz frequency range. Higher carrier
frequencies will allow for fast transmission of huge
amounts of data as needed for new emerging
applications. Despite the tremendous hurdles that have to
be overcome with regard to sources and detectors, circuit
and antenna technology and system architecture to
realize ultrafast data transmission in a scenario with
extensive transmission loss, a new area of research
beginto form [30-32].
Among the countries engaged in developing THz
technologies for diverse applications today, USA, UK,
Germany, China, South Korea, Japan, Russia, Taiwan
and some others are leading. Among the countries
developing their own cooled and uncooled IR FPA
technologies for commercial and military applications,
there are the USA, UK, Japan, Germany, South Korea,
Canada, China, Italy, Russia, and in small quantities –
some others. IR and THz technologies today and in the
nearest times will be among key technologies for
security systems, communications, space, biomedical
and food control applications, etc.
For insight in IR and THz applications, there exist
a large number of books where these questions are
developed deeply and thoroughly (see, e.g., [28, 33-
45]).
As a rule, biomedical imaging techniques are
considered as non-invasive methods for looking inside
the body without opening up the body surgically. There
are many medical imaging techniques (see, e.g.,
Table 1), every technique has different risks, limitations
and benefits and cannot be used as be individually
reliable in all biomedical applications [28, 46].
First of all, development of IR and THz
technologies are important in early cancer diagnostics, as
a cancer is one of the leading causes of death worldwide.
In 2012 there was 8.2 million death data vs. different
form of cancer [48]. Cancer is the second leading cause
of death and in 2015 was responsible for 8.8 million
deaths – nearly 1 in 6 global death [49]. The total
number of deaths due to cardiovascular disease read 17.3
million a year according to the WHO causes of death
2008 summary tables [50]. Thus, death data vs. different
form of cancer are comparable to cardiovascular diseases
and will continue to rise to over 13.1 million in 2030
[51] and the economic impact of cancer is significant
and increasing. The total annual economic cost of cancer
in 2010 was estimated at approximately US$ 1.16
trillion [49].
Among women, the breast cancer decease is one of
the prime causes of their death worldwide [42, 50].
Breast cancer patients diagnosed are characterized
into three cases: in the first case 90% patients diagnosed
will undergo surgery to treat the disease, in the second
case, 60% will undergo breast conserving surgery,
according to breast conserving surgery the primary
tumor is removed with a margin of normal tissue around
it and remaining mastectomy. Around 10–15% of
patients will require the second operation, as the margins
are not free of cancer on histopathology [52]. That’s why
more accurate technique is needed to assess resection
margins during surgery to avoid the next operation. In
the case of THz technology for cancer diagnostics, it is
conditioned with strong water absorption as water
concentration reveal a lot about the health of human
tissue, with water content in cancerous cells higher than
in healthy cells.
Thermography has a potential in screening the
breast cancer diagnostics detecting the growth of
malignant tumor due to increase of the internal
temperature captured by thermograms. Infrared
thermography has emerged in recent years as an
attractive and reliable technique to address complex non-
destructive (NDT) problems [53]. But in its applications
one should take into account that medical infrared
imaging can only be applied by physicians who have
been educated and trained intensively as well as have
received a medical certificate [54]. This is still valid
now.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
doi: https://doi.org/10.15407/spqeo20.03.273
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
277
Table 1. A comparison between the different biomedical imaging techniques (following [46]).
Image quality System availability Safety
Imaging
technique Spatial
resolution
Good
contrast Cost Real time
information
Ionizing
radiation
effect
Heating
effect
Radiography
(X-ray) 1 mm Soft tissue
and fluid Medium No Yes (active) Low
CT (X-ray) 0.5 mm Hard and
soft tissues High No Yes (active) Low
MRI (magnetic
and radio
frequency fields)
0.5 mm Hard and
soft tissues High No No (active) Medium
Ultrasonography 1 mm Soft tissues Low Yes No (active) Negligible
Elastography1) 200 µm Soft tissues Medium Yes No (active) Low
Optical 100 nm Soft tissues Low No No (active) Medium
Radionuclide 3 mm Soft tissues High No Yes (active) Medium
IR
(Thermography) 1.5 mm2) Soft tissues Low No No
(passive) No (passive)
THz
~50–1000 µm
(dependent on
wavelength)2)
Soft tissues High/Medium
(TDS/CW3)) No No (active)
Dependent
on radiation
power
1) Elastography imaging may be ultrasound elasticity imaging, magnetic resonance elasticity imaging, optical
elasticity imaging or tactile imaging.
2) Far-field approximation.
3) CW systems with photomixers.
The US Federal Communications Commission established maximum permissible exposure limits of 1 mW/cm2 for 6
min in the 30–300 GHz frequency range [47].
CT is the computerized tomography, MRI is the magnetic resonance Imaging, IR is the infra-red, THz is the
terahertz, TDS is the time delay spectroscopy, CW is the continuous wave. Active means the presence of radiation
source, passive means the analysis of radiation that is emitting from the object examined (e.g., thermography).
Today, potential and existing IR and THz
technology applications are broad in such diverse fields
as medicine, telecommunications, energy control, space
research, missile systems, and defense IR signature
analysis and measurement techniques, territory control
and security, etc. IR and THz technologies are well
developed for astronomy, military and surveillance
applications, Earth surface control, heat stress
diagnostics in industrial processes, thermal conductivity
of samples with IR thermography, breast cancer
diagnostics, thermography in semiconductor reliability
testing, control in building enclosures and art, tank levels
of liquids, automotive applications, gas analyzers (see,
e.g., [55-59]) and in biomedical applications mainly for
breast cancer diagnostics both in preclinical research
settings as well as in the clinical assessment of patients
(see, e.g., [28, 44, 45, 53, 60]).
In biomedical applications, IR technologies may
serve as one of the additional imaging methods (limited
as a primary breast cancer diagnostic [42, 46, 61]), as
compared to other better developed techniques.
Moreover, interpretations of thermographic images
depend on the specialists, which may lead to errors and
uneven results [42].
Application of THz waves to biomedical questions
is motivated by: (1) strong absorbance by water; (2)
rotational and vibration resonances in biomolecules; and
(3) low possibility of objects damage by low-energy
photons that unlike X-rays are not so harmful to the
tissues (see, e.g., [21, 45, 52]). However, many of the
reported THz effects under low-intensity radiation
produce a variety of bio-effects [2].
THz spectroscopy and imaging have a drawback
because of limited spatial resolution. Diffraction limit
(far field approximation) prevents light of a wavelength
λ from being focused to a spot (Airy disk diameter) with
a diameter of ∅ ≈ 2.44 λ (f /D) where f /D = F# is the f-
number of the optical system, f is the focus length and D
is the diameter of lens. At radiation frequency of 1 THz
and F# = 1 the Airy disk diameter ∅ ≈ 0.7 mm,
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
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© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
278
therefore, THz spectroscopy and λ (f /D) and microscopy
of objects is restricted to measurements of ensembles of
molecules. Imaging resolution will be restricted by
dimensions (l ≈ 1.22 λ (f /D)) over sample heterogeneity.
Therefore, there were developed some of microscopy
techniques that extend the scope of THz spectroscopy,
among which, e.g., there is scattering-type near-field
THz microscopy (see, e.g., [29, 62]).
In spite of great efforts in recent two or three
decades resulting in an exponential growth of the
number of publications [1, 3, 6, 36, 38, 39] THz
applications in general are still in early stage of
development, so many other potential applications in
future can be added to astronomy, biomedicine,
pharmaceutical, wireless communications, security,
package inspection, food industry, material studies,
spectroscopy, etc. (see Fig. 6). Also, THz absorption on
diluted soil samples can be effective in identifying soil
constituents, such as aromatic compounds, and soil
contaminants, such as pesticides [63].
4. Influence of radiation
THz waves have low photon energy to ionize atoms and
molecules, and this energy is much less to cause cancer
and genetic mutations. Other health effects can be
caused by thermal effects (temperature changes during
irradiation) under powerful THz radiation. But as it was
summarized, a couple decades ago that many of reported
THz effects under low-intensity radiation produce a
variety of bio-effects, a lot of which are quite
unexpected and can’t be explained by temperature
changes during irradiation [2].
As concerning the nervous tissue, only few studies
were performed in application to a living organism for
evaluationof transient effects in these spectral regions.
Using 60 GHz low-density short time (5 s) radiation
power (~4 mW/cm2) incident on the object, it was shown
that the real-time effects in isolated leech ganglions
could not mimicked by equivalent bath heating [65].
Therefore, it seems that the needs of THz radiation
effects researches on living organisms for determination
of THz and mm waves ultimate dosage and exposure
time are important for evaluation of the transient effects
on the health and for elaboration of safety standards.
THz imaging for human breast cancer diagnostics
is now less advanced as compared to thermography, and
further development of the technology and clinical
examination are needed to evaluate its feasibility in the
clinical environment [66]. Also, when carrying out THz
breast cancer diagnostics, it should be taken into account
the power level of radiation that can be harmful for
living objects as THz diagnostics is mainly possible for
active vision systems.
Widely-spread TDS spectroscopy and imaging
pulsed THz systems for biomedical applications has
started just after the publication [67] due to the
sensitivity of THz radiation absorption (see Figs. 1 and
2) to water content in tissue. The degree of hydration of
tissue could be used as a measure of disease state [67].
The typical spectral range of pulsed THz systems, as a
rule, is within ν ~ 0.1–4.0 THz with the peak frequency
~0.4 THz [12]. For pulsed systems the typical THz
source radiation power is lower or close to 0.1…1 μW in
dependence of illuminated power, radiation frequency,
semiconductor material used as a switch, etc.
Fig. 6. General scheme of explored and future THz spectroscopy and imaging applications [64].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
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Beside pulsed systems, there exist several possible
schematics of THz continuous wave (CW)
instrumentation. In the typical CW system a single fixed
radiation frequency or tuned in narrow frequency band
sources (e.g., IMPATT diodes, Gunn oscillators,
quantum cascade lasers (QCLs), BWO sources, gas
lasers, etc.) can be used. Broadband (ν ~ 0.1…2.5 THz)
radiation is possible to obtain applied photomixers,
where two lasers emit in two adjacent spectral ranges in
visible or near-IR regions. The photomixer translates the
laser beams of two lasers into THz radiation (frequency
domain THz radiation). For this kind of CW systems, the
radiation THz power, as a rule, doesn’t exceed 2 μW in
dependence of radiation frequency, semiconductor
material used as a photomixer, etc.
CW imaging allows for a more compact and simple
systems, while pulsed imaging measurements yield a
broader range of information, as it is also possible to
register the phase data in them.
In spite of potential capabilities at the moment,
THz imaging is limited to a great degree, as it could
distinguish the tumors and normal tissues, serious
inflamed and normal livers, but could not distinguish the
grade of tumors and inflammation [68].
Although THz waves do not penetrate far into the
body (from several hundred micrometers up to several
millimeters in dependence of fatty content), that is one
of the main drawbacks, it would be possible to project
THz endoscopically, as in optical coherence
tomography. Examples of diagnosis of cancerous tissues
with THz radiation are reported as they exhibit different
hydration levels from normal tissues [69, 70].
Terahertz spectra of tissues with a high water
content, e.g. skin, follow a similar trend as that for pure
water but the absorption is not as high [1]. Water
absorption limits the depth of tissue that may be imaged
using terahertz to a few hundred micrometers in skin and
up to several millimetersis tissue with more fat content
like breast.
Because of strong absorption by water in many
cases of applications to biomedical and food, THz
imaging and spectroscopic systems can be applied, e.g.,
for mapping tumor margins or surface of food products
with not a great depth but about 2 mm in breast because
fatty tissue [71, 72]). Moreover it was found the
frequency dependence of absorption coefficient on salt,
protein and DNA content. In addition THz water
absorption depends on protein structural changes, such
as ligand binding or denaturing [1].
Among the THz imaging and spectroscopy systems
for these purposes, there are mainly used such systems
as the THz pulse imaging – THz time domain
spectroscopy (TDS), and continuous wave (CW)
photomixer systems (see, e.g., [51]).
Today THz spectroscopy and imaging used in the
radiation frequency range ~0.1–4 THz require
femtosecond lasers and photoconductive broadband
antenna sources and detectors both for generation and
detection of THz radiation, respectively. They are the
most expensive components of the systems, and this is a
reason of healthcare cost as compared to other methods.
Still, the challenges of THz spectroscopy and imaging
applications lie in providing information not available
from other methods.
It was shown that an advance for enhancing THz
biomedical imaging can be reached by introducing
exogenous contrast agentsthat are capable to improve the
contrast. It was found that the THz reflection can be
increased in the cancer cells with gold nanoparticles [45]
upon their irradiation with an IR laser, or magnetic
induction heating of superparamagnetic iron oxide
nanoparticles [73], due to a rise in the temperature of
local water.
Biomedical diagnosis is based on both structural
and on functional data, as well as patient history and
subjective symptoms. Structural imaging methods are as
following: X-ray, ultrasound imaging, MRI (magnetic
resonance imaging), and the classical and electron
microscopy also fall into the imaging category.
Medical diagnostic with IR waves is a functional,
passive and non-invasive method for analyzing
physiological functions related to body thermal
homeostasis or organ temperature and, therefore, its
results cannot be directly compared to the results
obtained by structural imaging methods. It is used to
detect and locate temperature distribution characterized
by a non-physiological increase or decrease in
temperature at the body surface. Today, the improved
hardware detection systems with additional advanced
software solutions make it possible to incorporate
atomical and physiological information by image fusion,
which helps to generate information of affected areas. IR
thermography is used for measuring and analyzing
physiological functions and pathology related to the
body thermal homeostasis and temperature [74].
Since the middle of 20-th century, infrared (IR)
spectroscopy coupled to microscopy (IR
microspectroscopy) has been recognized as a non-
destructive, label free, highly sensitive and specific
analytical method with many potential useful
applications in various fields of biomedical researches
and, in particular, cancer research and diagnosis.
Although many technological improvements have been
made to facilitate biomedical applications of this
powerful analytical technique, it has not yet properly
come into the scientific background of many potential
end users. Therefore, to achieve these fundamental
objectives an interdisciplinary approach is needed with
basic scientists, spectroscopists, biologists and clinicians
who must effectively communicate and understand each
other’s requirements and challenges [59].
A lot of daily-used materials, such as clothing, dry
paper, plastics, dry leather etc., are transparent in this
wavelength range [22, 23] (paper, foams, plastic,
textiles, etc.). Many plastics are used now for 3D printed
THz optics [24] especially in CW systems. Table 2
presents the data for some plastic and other materials in
the THz spectral region.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 273-283.
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© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
280
Table 2. Parameters of some materials in the THz region (T = 300 K) important for THz optics.
Material Refractive index, n Absorption coefficient, cm–1 Reference
ABS 1.57 ≈ 1.5–25
0.2–1.5 THz
[24]
PLA 1.89 ≈ 1.5–25
0.2–0.9 THz
[24]
Nylon 1.72 ≈ 0.2–40
0.2–1.2 THz
[24]
Bendlay 1.53 ≈ 1.5–25
0.5–1.5 THz
[24]
Polystyrene 1.56 ≈ 0–4.5
0.2–1.5 THz
[24]
HDPE 1.53 ≈ 0
0.2–1.5 THz
[24]
PP 1.49 ≈ 0.1
0.2–1.5 THz
[24]
High-resistance Si 3.42 < 0.05
0.1–2.0 THz
[77]
Quartz 1.96 ≈ 1–9
0.1–2.0 THz
[76]
TPX ≈ 1.45, 0.3–2.5 THz 0.2–0.9, 0.3–2.5 THz [75]
Teflon-AF ≈ 1.39, 0.3–2.5 THz ≈ 0.2–3.4, 0.3–2.5 THz [75]
HDPE ≈ 1.53, 0.3–2.5 THz ≈ 0–2.4, 0.3–2.5 THz [75]
Teflon ≈ 1.435, 0.3–2.5 THz ≈ 0–2.4, 0.3–2.5 THz [75]
Here, ABS is the acrylonitrile butadiene styrene, PLA – polyactic acid, HDPE – high-density polyethylene,
PP – polypropylene, TPX – methyl-pentene copolymer (polymethylpentene), HDPE – high density polyethylene.
For some explosives, the data about absorption
coefficients are presented in [78].
The fact that THz radiation has a shorter
wavelength than microwave radiation and thus has the
capability of having a higher spatial resolution, and at
low levels of radiation power does not pose any known
harm to living organisms, makes THz imaging a
powerful and presumably safe imaging technology [12,
45, 65].
Unlike the pulsed THz imaging, the CW imaging
presented only yields intensity data and does not provide
any depth, frequency-domain or time-domain
information about the subject when a fixed-frequency
source and a single detector or arrays of detectors are
used. However, the CW imaging systems are sufficient
for many imaging applications affording a compact,
simple, fast and relatively low-cost system. Since it does
not require a pump–probe system and the complexity of
the optics involved, the optics of CW systems are much
simpler and thus their cost can be considerably reduced
as compared to pulsed THz systems [46, 79], and since it
does not require a time delay scan, image formation can
take place more quickly [12].
Compared to IR and microwave systems, THz
imaging, spectroscopy and communication systems and
their components (detectors, sources, etc.) are still
remaining less developed. That is a reason why at the
moment THz wave instrument capabilities are still away
in comparison, e.g., with IR or microwave system
feasibilities.
For insight in applications, there exist a large
number of books in which the topics pointed out shortly
are developed deeply and thoroughly (see, e.g., [9, 28,
33-39].
5. Conclusion
IR and THz technology applications today are broad in
such domains as astronomy, military and surveillance,
telecommunications, security, energy and food control,
but it seems one of the most topical are biomedical
applications, e.g., for breast cancer diagnostics, colon
cancer, burn imaging, etc., especially in the cases where
there is a need of accurate location of tumor margins
when conservation of normal tissue is required. It can be
expected that potentiality of these technologies will be
only in progress in diverse directions in biological and
medical fields. Further work is needed for scientific
challenge to provide information not available from
other techniques. One of the main barriers in providing
healthcare conclusions by using THz technologies is the
cost of THz pulse imaging and spectroscopy
instrumentation that is mostly related with a high cost of
short pulse lasers needed for their applications.
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© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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|
| id | nasplib_isofts_kiev_ua-123456789-214957 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-19T04:21:08Z |
| publishDate | 2017 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Sizov, F.F. 2026-03-05T12:06:00Z 2017 Infrared and terahertz in biomedicine / F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 273-283. — Бібліогр.: 79 назв. — англ. 1560-8034 PACS: 87.50.U-, 87.64.km, 87.80.Dj, 87.85.Ox https://nasplib.isofts.kiev.ua/handle/123456789/214957 https://doi.org/10.15407/spqeo20.03.273 A number of potential advances of infrared and terahertz technologies in application mainly to biomedicine are shortly discussed. In spite of the fact that there are a number of well-established imaging and spectroscopic techniques in application to biomedicine, there exist some problems where IR and THz technologies are the challenging technologies that can provide information not available from other techniques. E.g., they can be applied in cases where there is a need to improve the surgical removal of cancer, strictly locating tumor margins when conservation of normal tissue is needed. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Infrared and terahertz in biomedicine Article published earlier |
| spellingShingle | Infrared and terahertz in biomedicine Sizov, F.F. |
| title | Infrared and terahertz in biomedicine |
| title_full | Infrared and terahertz in biomedicine |
| title_fullStr | Infrared and terahertz in biomedicine |
| title_full_unstemmed | Infrared and terahertz in biomedicine |
| title_short | Infrared and terahertz in biomedicine |
| title_sort | infrared and terahertz in biomedicine |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/214957 |
| work_keys_str_mv | AT sizovff infraredandterahertzinbiomedicine |